Five Years of Drought

Why we love it

This award-winning set of maps sets a new standard in analysis and visual storytelling. The bivariate+hexbin mapping technique proves to be as gorgeous and sophisticated as it is intuitive. We love how these maps capture the geographic and historic complexity of this epic US drought. Combining five years of weekly data, the maps uncover how conditions vary in both intensity and length. Colour indicates severity while size indicates frequency. For example, large deep purple symbols indicate where exceptional drought was experienced almost continuously for five years. This is geographic analysis at its best.

Why it works

The main map stands on its own while supplemental maps give a different perspective on the same data. This works because it adds nuance to the story and shows the care taken by the mapmaker. It also highlights that there is no single “best” way to tell a story. The judicious use of call-outs directly on the maps, the powerful legend, and the minimal-yet-elegant basemaps combine to turn a big, messy dataset into understanding. Wise use of an equal-area projection ensures each hexbin indicates the same sized area. A companion blog post explains how anyone can re-use this work.

Important steps

Prepare data for use

Download, merge, and weight the raw weekly data into a single five-year aggregate.

Create a bi-variate map

Requirements

Data

Shapefiles that delineate the contours of drought severity are produced and archived each week by the United States Drought Monitor. US state outlines and terrain came from ArcGIS Living Atlas of the World. Software used: ArcGIS Pro, Story Map Cascade Template.

Analysis

Use the Merge tool to merge individual weeks of data into a single shapefile. Use the generate tessellation tool to convert multiple overlapping drought severity polygons into a hexagon tessellation scheme weighted by source data (by both severity and frequency).

Time

Some unknown amount of time was spent in downtime-daydreaming and playing around with color palettes and cell sizes. Actual production time of the physical map was around five hours, including some exploratory dead ends. It took a further day to craft the story map and blog.

Tips and tricks

Create seamless switches when user zooms

The interactive version of the map seamlessly switches to graduated numbers once the user has zoomed in far enough to show local details.

Show intense drought areas by grouping circles

Size the graduated circles so the largest just start to coalesce into a single blob of drought.

Use hillshading to give basic orientation

The elegant and restrained basemap with hillshading provides enough information to orient the reader but keeps the focus on the thematic cartography.